<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var shu=prompt('请输入一个年份')
        // 根据年份判断
        if(shu%4==0 &&shu%400==0){
            alert('闰年')
        }else{
            alert('不是')
        }
    </script>
</body>
</html>